The tretment of contaminated waste water from municipal or industrial sources involves a sequence of processing steps for maximizing water purification at minimum costs. Industrial effluents, particularly waste water from oil refineries, include a broad spectrum of contaminants, and, consequently, such waste water is usually more difficult to decontaminate than waste water from municipal sewage systems. Four main sequential process treatments are used to decontaminate such industrial effluents although similar treatment is given municipal effluents, or combined municipal/industrial effluents. These are a primary, intermediate, secondary, and tertiary treatments. The primary treatment calls for removal of gross amounts of oil and grease and solids from the waste water. In the oil industry, usually separators of American Petroleum Institute design are employed from removal of free, separable oil and solids. In municipal waste water treatment, generally little free oil is present but solids removal is still needed. The intermediate treatment is the next process and it is designed to adjust water conditions so that the water entering the secondary treatment zone will not impair the operation of the secondary treatment processes. In other words, intermediate treatment is designed to optimize water conditions so that the secondary treatment process will operate most efficiently. The secondary treatment calls for biologically degrading dissolved organics and ammonia in the water. One of the most common biological treatment processes employed is the activated sludge process discussed below in greater detail. The tertiary treatment calls for removing residual biological solids present in the effluent from the secondary treatment zone and removing contaminants which contribute to impairing water clarity or adversely affecting water taste or odor. This is usually a filtration of the water, preferably through beds of sand, or combinations of sand and coal, followed by treatment with activated carbon. In some cases, air flotation can be used as an alternative to filtration.
The activated sludge process is a conventional waste water treating process which produces the highest degree of biological treatment in reasonably compact facilities at the present time. The application of this process to the treatment of industrial waste water has, however, been slow compared with municipal applications. Industrial applications of this process are nevertheless increasing rapidly. Currently, the activated sludge process is capable of achieving reduction in the five-day biological oxygen demand (BOD.sub.5). However, the BOD.sub.5 contaminants present in industrial waste water are relatively small compared with the total oxygen demanding contaminants present in such waste water as measured by the chemical oxygen demand (COD) test. For example, the BOD.sub.5 contaminants present in the effluent from an activated sludge process typically ranges from 10 to 20 parts per million parts of water. It is not uncommon to also find present in such effluent 10 to 20 times this amount of COD.
The activated sludge process generally has two, three or four stages of treatment. In the first stage, contaminated water is contacted with the activated sludge. The sludge includes micro-organisms which feed on the contaminants in the water and metabolize these contaminants to form cellular structure and intermediate products. This decontaminated water flows into a second clarifier stage where suspended sludge particles are separated from the decontaminated water. A portion of the sludge is recycled to the first stage and the remainder is forwarded to the third and fourth stages. This sludge forwarded to the third and fourth stages includes water. In the third stage the sludge is thickened to remove excess water and in the fourth stage the thickened sludge is permitted to digest, that is, the micro-organisms feed upon their own cellular structure and are stabilized.
Recently, the importancce of powered activated carbon in waste water treatment is being realized. However, the use of powdered activated carbon has often been uneconomical because of under utilization of a given amount of carbon.
Many processes have wasted powdered activated carbon along with sludge prematurely.
Many industries have extremely strong wastes having a COD in excess of about 1000 mg/l. In some industries such as paper or chemicals, COD of about 10,000 mg/l is not uncommon. A process for the treatment of such strong wastes must be integrated in that each part of the purification process will cooperate in order to achieve maximum purification at low cost. It must also make full use of powdered activated carbonn without undue waste.
It is an object of this invention to provide a waste water process which produces high quality effluent, especially when treating strong wastes.
It is an object of this invention to provide a waste water process which makes efficient use of powdered activated carbon.
It is an object of this invention to provide an integrated waste water treatment process which reduces the amount of powdered activated carbon needed thereby making efficient use of said carbon, and produces a high quality effluent.